Igniter device



Dec. 5, 1961 s. GoRDoN IGNITERDEVICE Filed sept. 29, 195e ATTORNEYS.

3,011,441 Patented Dec. 5, 1961 dice a corporation of Great Britain Filed Sept. 29, 1959, Ser. No. 843,284 3 Claims. (Cl. lill-70) This invention is concerned with an igniter device which is suitable for use in igniting the soli-d fuel propel'lants of rocket motors.

It has been the practice to use for the ignition of solid fuel propellants for rocket motors an igniter device having a separate primary means of ignition and comprising a dished steel head boss or plate into which is sealingly fitted a plastic container containing the igniter composition, the upper surface of the container being closed by a plastic bursting disc. The primary means of ignition is separated from the igniter composition until a sensitive initiating means is fired. This improves the overall safety of the rocket motors and also avoids the possible ignition of the sensitive initiating means as a result o-f electrical field energy picked up by the necessary lead wires to the sensitive initiating means. The dished steel head boss or plate has a primary ignition passagecommunicating with the igniter composition contained in the plastic container and the Idepth of penetration of the igniter composition into the primary i-gnition passage is determined by a plastic sealing disc which lits across the passage. At the other end of the primary ignition passage there is a suitable sensitive initiation means such as a low tension fuse-head or a low tension fuse-head with a delay element, with or without the addition of a small incremental charge of black powder. Upon firing, the sensitive initiation means spits incandescent particles, flame and hot gas through the thin plastic sealing disc to ignite the igniter composition. The burning of the igniter composition in turn ignites the solid propellant charge.

It has been found that under operating conditions such an igniter device sets up shock conditions on firing of the rocket motor. This ignition shock comprises an extremely rapid build-up of pressure and thrusts to levels which are greatly in excess of the normal operating levels for the rocket motor. Under such conditions the following possibilities may arise:

(a) The extremely rapid application of very high pressure may fracture the main propellant charge resulting in motor failure through excessive pressure development or malfunctioning, i.e. the motor may burst because mechanical stresses may become excessive and greater than design limitations because of greatly increased pressure arising from the extra exposed propellant surface due to charge fracture. This is particularly -likely under cold conditions when propellant in general becomes cornparatively brittfle. Even if such a severe failure is not incurred, charge fracture will lead inevitably to departure from the thrust/time programme required by the motor design and thus to failure of the missile to comply with test flight requirements.

(b) The mechanical loading imposed upon the motor body or transmitted through it to the missile may cause mechanical failure or malfunctioning.

(c) Mechanical or electrical parts may become overstressed and fail to function as required by design.

One way of reducing the severity of ignition shock is to reduce the quantity of igniter composition. However, when this is done to such an extent as to bring the functioning of the ignition within tolerable limits of pressure and thrust at high temperatures, unduly prolonged delay intervals. are obtained under ambient, and especially low. temperature conditions and complete misres may be experienced.

According to this invention there is provided a device for securing ignition of solid fuel propellants for rocket motors comprising a housing forming or carrying a container for igniter composition, a bursting disc forming a closure for said container and serving also to separate said composition from the solid fuel, and a primary ignition passage in the housing for securing ignition of the igniter composition by means of a detonator, fusehead or the like, characterised in that a transfer tube,

the walls of which extend into the container and are surrounded by the igniter composition, and which transfer tube opens near one end into the igniter composition near the bursting disc and communicates at its other end with the primary ignition passage.

iin a preferred form of the invention the transfer tube is closed at that end adjacent Ito the bursting disc and is open to the igniter composition through peripheral ports situated close to said closed end.

Conveniently, in order to prevent any igniter composition passing into the transfer tube and consequently into the primary ignition passage, a thin membrane of cellulosic material may be used to close the periphera-l ports.

A preferred form of the invention lwill now be described with reference to the accompanying drawing which illustrates a sectional elevation of the igniter device.

Referring to the drawing, the igniter device comprises a dished steel housing 1, having a primary ignition passage 2 which is normally closed at one end by a blanking plug 3 but which, prior to firing, is replaced by a iring-puffer (not shown). The igniter composition 4 is contained within a plastic container 5 which sealingly engages as at 6, 7 with the dished steel housing, the igniter composition being held within the container by a plastic bursting disc 8. A metal or plastic transfer tube 9 communicates at one end with the primary ignition passage, its other end terminates near to the plastic bursting disc 8. This transfer tube 9 has at the end portion adjacent the bursting disc 8, four ports, one of which 10 is shown in the drawing. In order to prevent the igniter composition falling into' the transfer tube, these ports may be closed by a thin membrane of cellulosic material.

In operation, the blanking plug is replaced by a tiringpuffer. When the tiring-puffer 1s operated, the initiating spit of incendiary particles, ame and hot gas travels along lthe primary ignition passage and along the transfer tube, and initiates ignition of the igniter composition from the four ports 10. Thus ignition of the igniter composition occurs at the surface of the igniter composition in the region of the bursting disc 8 and adjacent the solid propellant and the igniter ,composition burns smoothly without the development ofany excessive pressures and thrusts and there is no resulting excessive mechanical loading on the propellant charges or the rocket motor structure.

I claim:

1. A device for securing ignition of solid fuel propellant in a rocket motor, comprising: a housing; a container; means for securing said container in said housing; an ignited composition Vdisposed within said container; a bursting disc secured to said container opposite said housing for closing said container; means defining a primary ignition passage extending through said housing and opening 4to said container; a transfer tube having its bore aligned and communicating with said passage, said tube extending substantially through said igniter composition and terminating closely adjacent said bursting disc; and means providing for communication between Said bore and said igniter composition adjacent said bursting disc, whereby said igniter composition may be ignited in the region of the bursting disc. 5

2. A device as defined in claim 1 wherein the end of Said tube is closed, and said communication means includes peripheral ports in the tube.

3. An ignter device according to claim 2, in which a thin mebrane of cellulosic material is used to close the 1D peripheral ports.

References Cited in the le of this patent UNITED STATES PATENTS Hathaway Oct. 18, Sarge Aug. 10, Sheehan Dec. 7, Loeb May 1, Kane Ian. 29, Smith June 4, Casati Sept. 23, Gey Feb. 10, 

